The Great Pacific Garbage Patch, a rotating soup of plastic in the north Pacific Ocean, contains up to 16 times the amount of waste than previously thought.

Key points

Surveys of the Great Pacific Garbage Patch conducted in 2015 and 2016 estimate 78,200 tonnes of plastic waste are packed into an area almost the size of Queensland

This figure is much greater than previous estimates and has increased exponentially since the 1970s

Scientists were surprised to find that most of the mass was made up of larger pieces, such as fishing debris

That’s the conclusion of a team of scientists who’ve conducted what is claimed to be the most comprehensive study of the patch’s size and the debris floating in it to date.

Using combination of drag netting and visual surveys from boats and an aeroplane, they estimated the patch is 1.6 million square kilometres in area — almost the same size as Queensland.

Packed into this area is more than 78,000 tonnes of plastic, the researchers report in the journal Scientific Reports.

Most of the mass was made up of pieces larger than 5 centimetres. While microplastics, which account for about 8 per cent of the mass, made up a bulk of the estimated the 1.8 trillion pieces of plastic floating in the patch.

Researchers estimate there are about 1.8 trillion individual pieces of plastic in the patch.

(Supplied: The Ocean Cleanup)

Researchers estimate there are about 1.8 trillion individual pieces of plastic in the patch.

Supplied: The Ocean Cleanup

Lead researcher Laurent Lebreton said the garbage patch was growing exponentially and was boosted by debris washed out to sea during the Japanese tsunami in 2011.

“We show that plastic concentration has been increasing exponentially since the 1970s for different reasons,” said Dr Lebreton, an oceanographer at the Ocean Cleanup Foundation in the Netherlands.

“We found about 30 per cent of the identifiable objects were likely coming from Japan.

“We correlated that with our model and we looked at estimates from the Japanese Government in terms of how much they think was washed to sea that day… and we predict that about 10-20 per cent of the materials post-2011 in the larger size class came from the tsunami.”

Researchers used nets for surface sampling as well as an aerial survey.

(Supplied: The Ocean Cleanup)

Researchers used nets for surface sampling as well as an aerial survey.

But Dr Lebreton said that this method excludes larger debris that cannot be collected by the nets, and that boat surveys can only cover a limited area.

“We saw that the surface area sampled by our trawls was not really large enough to be representative of the contribution of the bigger debris,” he said.

“[So] we decided … to conduct an aerial expedition above the patch. We collected about 7,000 images [from the plane] and that helped us to calculate the contribution of larger debris such as ghost nets.”

Clean-up operation needs to target source

By including the larger debris sizes in their study, the researchers knew they’d come up with a bigger figure than previous studies, but they were still surprised by just how much mass the larger debris contributed.

“I wasn’t expecting to find that 92 per cent of the mass would be [larger plastics],” Mr Lebreton said.

Almost half the larger debris they identified was commercial fishing gear including nets and fish aggregation devices — nets and other structure set adrift intentionally by fishers to attract fish.

Research scientist Dr Denise Hardesty from the CSIRO said it wasn’t surprising the survey produced a much larger size estimate of the garbage patch, given the different research methods used.

“When you’re comparing aerial surveys that are looking at ghost nets with estimates that are all focused on floating plastics we’re not really making the exact same comparison,” said Dr Hardesty, who was not involved in the study.

“Ghost nets will weigh so much more than all those little tiny bits and pieces and fragments.”

But she says that the new research is still cause for concern.

“Whether you’re focusing on count or mass, I think it is alarming and we all recognise that this is an increasing global project and it’s going to take local solutions as well as hopefully global governance to help resolve the issues,” she said.

“We need to deal with this before it enters the ocean rather than when it’s out in the middle of the ocean.”

Plastic circulating in the garbage patch does eventually get “kicked out” and washes up on coastline, Dr Hardesty said.

But right now we are feeding waste in at a much higher rate than it can be expelled.

“There’s an increasing source that’s coming from our coast. And yes shipping and fisheries waste is also contributing, but the lion’s share of mismanaged waste is coming from land,” she said.

The Ocean Cleanup Foundation said they would use the research to develop technologies that, they claim, would be able to “clean up 50 per cent of the Great Pacific Garbage Patch in five years”.